Method of making a profiled element having a surface layer for reducing the coefficient of friction between the profiled element and a glazing surface

ABSTRACT

A wiping strip for a motor vehicle screen wiper is in the form of a profiled element of vulcanised material consisting of rubber or an elastomeric material, having a surface layer for reducing the coefficient of friction between the wiping strip and a glass surface to be wiped. The surface layer is formed by immersion of the profiled element in a solution, or by exposing the profiled element to the solution in atomised form. The solution consists of a solvent with a powder, such as graphite, dispersed in it. The step of forming the surface layer is carried out during the step of vulcanising the material of the profiled element.

FIELD OF THE INVENTION

This invention relates to a method of making a profiled element fromrubber or an elastomeric material, natural or synthetic, the materialbeing vulcanized and having a surface layer which is adapted to reducethe coefficient of friction between the profiled element and a surfaceof a glazing element (for example a vehicle windshield) over which theprofiled element is to be passed in wiping motion. A non-limitingexample of such a profiled element is a wiping strip for a motor vehiclescreen wiper.

The invention also relates to such a wiping strip, when made by such amethod.

BACKGROUND OF THE INVENTION

In a known technique, a profiled element of the general kind definedabove, for example a motor vehicle windshield wiper wiping strip, isclad with a lubricating coating, which is obtained by immersing thewiping strip in a solution in which a powder, such as graphite forexample, is immersed, or by applying this solution in atomised form tothe profiled element.

In this known technique, the lubricant coating is formed by immersingthe wiping strip in a solution which consists essentially of an acrylicresin binder in which the graphite powder is dispersed, or by applyingthe same solution in atomised form on the profiled element. Afterapplication of this solution, the wiping strip is dried so as to producea surface layer which gives the wiping strip properties whichconsiderably improves the quality of the wiping action performed by thewindshield wiper in which the strip is later incorporated. Although sucha coating does improve wiping quality, it has the disadvantage that itis particularly fragile, and in particular it has a very low resistanceto detergents and other cleaning agents which are typically employed inthe washing of vehicles. As a result, the lubricant coating has a veryshort useful life, in that it rapidly deteriorates and even disappearscompletely, thus quickly reducing wiping performance.

OBJECT OF THE INVENTION

The object of the invention is to provide a novel method for forming thesurface layer of a profiled element such as a wiping strip, as definedabove, which overcomes the above mentioned drawback by producing alow-friction surface layer of improved durability.

STATEMENT OF THE INVENTION

According to the invention, a method of making a profiled element ofrubber or an elastomeric material, the profiled element being vulcanizedand including a surface layer for reducing the coefficient of frictionbetween the profiled element and a surface of a glazing element, inwhich the surface layer is formed by immersion of the profiled elementin a solution in which a powder, in particular crystalline graphite, isdispersed, or by application of the said solution in atomised form on tothe profiled element, is characterised in that the step of forming thesurface layer is carried out during the vulcanization of the profiledelement.

DISCUSSION OF THE INVENTION, AND DESCRIPTION OF PREFERRED EMBODIMENTSTHEREOF

In the method of the invention, the solution which is employed typicallyconsists essentially of a solvent in which the powder is dispersed. Thepowder is preferably a crystalline graphite powder, the particle size ofwhich preferably lies in the range between 1 and 10 microns.

In general terms, in the method having features of the presentinvention, the solvent in which the profiled element is immersed, orwhich is applied in atomised form to the profiled element, causes thematerial, consisting of rubber or an elastomer, to undergo, duringreticulation of the material in the vulcanising step of the process, aswelling effect in the manner of a sponge. What happens here is that thecavities in the material become dilated during this process, and arefilled with the particles that constitute the lubricant powder.

The profiled element may, by way of non-limiting example, be a wipingstrip for a motor vehicle screen wiper.

After the evaporation of the solvent, and at the end of thevulcanization process, or during an intermediate drying step which mayif desired be interposed between the immersion of the profiled elementin the treatment solution (or the application of this solution inatomised form to the profiled element), the solvent evaporates; and thepowder particles are trapped in the surface pores, thus constituting adurable surface layer which is doped with powder to a depth of about 6to 12 microns.

The immersion step may be carried out by plunging the profiled elementinto a bath of the solution in liquid form, or by applying a mist of thesolution, i.e. an atmosphere saturated with droplets of the solution, tothe profiled element.

The application of the solution is preferably carried out while theamount of reticulation in the rubber or elastomer material is less thanabout 80%. Preferably, a phase of the vulcanization step is selected, inthe course of which the amount of reticulation in the rubber orelastomeric material is increasing continuously but is in the rangedefined between 10% and 80%.

The solvent itself may be of any one of various compositions. It may beselected from, for example, alkanes, alkenes, or aromatic, aliphatic andsimilar compounds.

The immersion of the profiled element in the solution, or theapplication of the solution in atomised form to the profiled element,may be carried out in a single step, or in the form of two or moresuccessive applications, in solutions based on solvents which areidentical to each other or different from each other, and in which thelubricant powders may be of different compositions and/or may have thesame particle size or different particle sizes.

The powder preferably consists of a graphite powder, but it could bereplaced or augmented by a powder of another low friction compound, suchas polytetrafluorethylene, molybdenum disulphide, and so on.

The method of the invention produces a surface layer which is verystrong and highly resistant to wear, and which is also hydrophobic.

The application of graphite to profiled elements, particularly motorvehicle screen wiper wiping strips, carried out by the method of dopingthe surface layer in accordance with the invention, has the furtherparticular advantage that it is carried out before two wiping strips areseparated from each other by cutting, when the latter are extrudedsimultaneously and joined together through their respective wipingedges. The narrow wiping edge of each strip, having been formed by thiscutting step, does not itself therefore have a surface layer doped witha lubricant agent. This facilitates turning of the wiping strip at theend of each stroke of the alternate wiping operation by the wiper.

In accordance with a further feature of the invention, the method of theinvention may further include a final step which is carried out afterthe rubber or elastomeric material has been fully vulcanized, this finalstep consisting of brushing the surface element that includes thesurface layer. The brushing step is for example carried out by passingthe profiled element longitudinally between two adjacent rotatingbrushes. These brushes are rotated in opposite senses or directions ofrotation. The direction of rotation of each brush is preferably suchthat the brush, where it makes contact with the profiled element, doesso in a linear direction opposed to the linear direction in which theprofiled element is advanced between the brushes.

The complementary brushing step homogenizes the surface coating of theprofiled element, and prevents the coating having defects in its outwardappearance, or other defects such as irregularities within itsthickness, or indeed adhesion faults. In this connection, it isdesirable to eliminate all of these defects, because where they existthey give rise to the risk of causing stripes to be produced during thewiping operation (where the profiled element is a screen wiper wipingstrip); such force can also lead to local deposits of graphite on theglass being swept, and to other undesirable effects.

Thus, the brushing step removes any excess graphite, eliminates graphiteparticles which are adhering poorly to the profiled element, andhomogenizes the graphite particles, by orienting the graphite plateletsin the same direction. The brushing operation also enables the presenceof the coating to be seen, because brushing alters the appearance of thecoating by changing its colour from matt black to a metallic grey shade.

The brushes may be replaced by brushing rollers made for example of feltor a suitable porous material. These rollers, if used, have profileswhich are complementary to that of the profiled element being treated.

In another version of the method according to the invention, thebrushing step may be replaced by an equivalent operation in which highpressure water jets are sprayed on the coated profiled element.

What is claimed is:
 1. A method of making a profiled element made of amaterial selected from the group consisting of rubber and elastomericmaterials, the method comprising:vulcanizing the material, wherein thevulcanizing includes reticulation of the material, and forming a surfacelayer on the material during the vulcanizing, the forming comprising:swelling the material to create a plurality of surface pores by applyinga first solution containing a first powder of anti-friction materialdispersed in a first solvent trapping the first powder in the surfacepores.
 2. A method according to claim 1, wherein forming the surfacelayer is performed before an amount of reticulation of the materialreaches 80%.
 3. A method according to claim 1, wherein forming thesurface layer is performed while an amount of reticulation of thematerial is increasing and is in the range between 10% and 80%.
 4. Amethod according to claim 1, wherein forming the surface layer comprisesimmersing the material in the first solution.
 5. A method according toclaim 1; wherein forming the surface layer is performed by applying thefirst solution in atomized form to the material.
 6. A method accordingto claim 1, wherein the first powder comprises particles having aparticle size between 1 and 10 microns.
 7. A method according to claim1, further including drying the material having the solution appliedthereon prior to the drying, thereby evaporating the first solvent,before the end of the vulcanizing.
 8. A method according to claim 1,further including brushing the profiled element after the vulcanizing.9. A method according to claim 8, wherein brushing comprises passing theprofiled element longitudinally between two adjacent brushes rotating inopposite directions of rotation.
 10. A method according to claim 9,wherein during the brushing, the profiled element is passed between thebrushes in a first direction, the brushes being rotated in directions ofrotation such as to make contact with the profiled element in a seconddirection opposite to the first direction.
 11. A method according toclaim 8, wherein the brushing is carried out by passing the profiledelement between two rollers having profiles complementary to that of theprofiled element.
 12. A method according to claim 1, further includingprojecting water jets on to the profiled element after the vulcanizing.13. A method according to claim 1, further including forming anadditional surface layer on the material during reticulation includingapplying to the material a second solution, the second solutioncomprising a second powder of anti-friction material dispersed in asecond solvent.
 14. A method according to claim 13, wherein the firstsolution and the second solution are different.
 15. A method accordingto claim 14, wherein the first powder and the second powder aredifferent.
 16. A method according to claim 14, wherein the first solventand the second solvent are different.